CN101369884A - An industrial wireless communication method based on adaptive channel hopping within a time slot - Google Patents

Abstract

The invention claims to protect a communication method based on self-adaptive channel hopping within a time slot, which belongs to the technical field of industrial wireless communication. Aiming at the fact that the prior art cannot realize self-adaptive channel hopping within the allocated time slot, the present invention realizes adaptive switching from the interfered preferred channel to the standby channel within the allocated time slot, and the sender adopts the CCA mechanism to monitor the communication channel. Interference, no data will be sent, and after the specified CCA monitoring time of this time slot, it will automatically switch to the standby channel to send data. The channel jumps to an alternate channel to wait for data to be received. At the same time, according to whether adaptive channel hopping is performed, time synchronization can be performed on the preferred channel or the standby channel. The invention of the sender can fully improve the channel utilization rate and success rate; improve the reliability and real-time performance of data communication; reduce data retransmission and reduce the extra load of the network; and meet the needs of the industrial wireless communication field.

Description

An industrial wireless communication method based on adaptive channel hopping within a time slot

technical field

The invention belongs to the technical field of wireless network communication, and relates to a communication method in an industrial wireless network, in particular to an industrial wireless communication method based on self-adaptive channel hopping within a time slot, and the method is especially suitable for industrial wireless networks.

Background technique

At present, industrial wireless communication is called a revolutionary technology in the field of industrial control. It is another hot technology in the field of industrial control after fieldbus. It is the most potential technology to reduce automation costs and improve the application range of automation systems. A new growth point for industrial automation instrumentation in 2019. Industrial wireless systems (such as wireless HART and ISA100.11a) that have attracted widespread attention in the world usually use TDMA and FDMA technology, that is, if two wireless nodes want to communicate data, the system will allocate a communication link ( Link), each communication link includes a communication channel (Channel) and a time slot (Slot), and the communication parties complete the communication according to the given channel within the specified time slot time, that is, the slot hopping channel technology, without considering the time Intra-slot hopping channel technology. Wireless communication systems such as Global System for Mobile Communications (GSM), Cellular Digital Packet Data (CDPD), and Bluetooth (Bluetooth) have widely used frequency hopping technology to improve the stability and reliability of communication. However, these systems are mainly based on Frequency hopping (channel hopping) between time slots of TDMA basically does not involve adaptive channel hopping technology.

Existing intra-slot communication mechanism: Both the sender and the receiver will adjust to a given communication channel at the beginning of the time slot. The sender monitors the channel through CCA before sending data. If the channel is busy, the channel may be interfered or blocked. If other nodes are occupied, if data is still sent at this time, a conflict will inevitably occur, so usually the sender will give up the subsequent time of this communication time slot. If the receiving party does not receive the information sent by the sending party within an acceptance waiting time, it will also give up the subsequent time of this communication time slot. The two parties in the communication did not successfully complete the communication within this communication time slot, and can only wait for the next allocated time slot to retransmit, which will lead to weak anti-interference, low reliability, low communication channel utilization, and transmission delay. shortcoming.

Contents of the invention

Aiming at the above-mentioned defects of the prior art, the technical problem to be solved by the present invention is to provide a highly reliable, real-time industrial wireless communication method for adaptive channel hopping in a time slot, which has the advantages of self-adaptive, high reliability, real-time Strong performance and high efficiency. For some applications with high comprehensive requirements (such as the field of industrial monitoring), the method can further improve the reliability of wireless communication by using the self-adaptive channel hopping technology within the time slot, and ensure the real-time and certainty of data transmission. In addition, for the industrial wireless time slot communication method, the present invention correspondingly proposes a receiver-based time synchronization method and algorithm, which has the advantages of high efficiency, simple time, low consumption of system resources, and reduced power consumption.

For each communication link in the wireless network, the system assigns two (or more) communication channels to it, one is the preferred channel, and the other is the backup channel. Time synchronization is performed on the preferred channel or the backup channel, and the time slot communication starts The CCA detection time length and the waiting time length for receiving data in the time slot have been negotiated before. At the beginning of a given communication time slot, both the sender and the receiver select the preferred channel for communication. If the communication channel is interfered, the sender monitors whether the channel is free through the CCA mechanism before sending data. If the channel is busy, the communication is considered The channel is disturbed and no data is sent. When the CCA monitoring time expires, it is generated as a judgment condition and the channel switching control command is executed; the receiver has been monitoring the channel. If it has not received data from the sender within the specified receiving waiting time, when When the receiving waiting time is overtime, it is determined that the channel is interfered with as a judgment condition, and the channel switching control command is automatically generated and executed. After the length of waiting time for data reception determined through negotiation, the sender and the receiver jump to the standby channel respectively, and after a channel switching period, a new round of communication process starts. The sender preferably performs channel monitoring again on the spare channel, and uses the spare channel for communication if the channel is not disturbed. If the channel is also interfered, the communication time slot can only be abandoned. All this process can be completed within the assigned time slot, without occupying other time slots additionally. The control command for channel switching is generated and executed by the two parties themselves, instead of one party sending the control command to the other party, so as to realize the self-adaptive channel hopping of both parties.

This method also supports the way of assigning multiple spare channels to the communication link. If the first two channels are disturbed and unavailable, they can continue to jump to the subsequent channel for communication, so as to further improve the reliability and success rate of communication. All this process is completed within the allocated time slot, without occupying additional other time slots. If a backup channel is selected, the backup channel can become the preferred channel in the future link, which can be more flexible and dynamic adaptive anti-jamming, and can further improve efficiency, reliability and real-time performance .

Therefore, this method can automatically resist problems such as channel interference in network communication through self-adaptive channel hopping, and has the following main advantages: 1. Flexibility and dynamic adaptability; 2. Can fully improve communication channel utilization and success rate; 3. Improve the reliability and real-time performance of data communication; 4. Reduce data retransmission At this time, reduce the additional load of the network;

In addition, in order to improve the utilization rate of the channel in the existing industrial wireless network system, the length of the communication time slot is usually just enough for a complete communication, but to realize the method of the patent of the present invention, it is necessary to reserve time for the second communication in a short time. In the existing time slot length, time can be saved through the following two main methods: (1) minimize the time error; (2) shorten the waiting time for receiving data. Both of these two measures need to be based on an accurate and efficient time synchronization method. Therefore, the present invention proposes a receiver-based time synchronization method for intra-slot self-adaptive channel hopping communication. In this method, the sender does not need to record a time stamp when sending, and then wirelessly sends to the other party, which can reduce the amount of data transmission and thus reduce power consumption.

The disadvantage of the present invention is that a spare channel needs to be allocated for each link, which reduces the capacity and bandwidth of the entire network system, and in a sense, sacrifices network capacity in exchange for high reliability and real-time performance of link communication. For some wireless network systems (such as industrial wireless monitoring network) with small network capacity and high requirements for reliability, real-time and certainty, the wireless communication method of self-adaptive channel hopping in this time slot provided by the present invention is particularly suitable , which meets some key technologies in industrial wireless communication, and will play a strong role in promoting the performance improvement and practical application of industrial wireless networks. In addition, the receiver's time synchronization method based on the self-adaptive hopping channel in the time slot proposed by the present invention provides strong technical support for the realization of the present invention, and partially solves the key problems faced by the self-adaptive channel hopping communication method in the time slot. question.

Description of drawings

Figure 1: Schematic diagram of an industrial wireless time slot communication model for adaptive channel hopping within a time slot

Figure 2: Sender Processing Flowchart

Figure 3: Receiver processing flowchart

Detailed ways

The industrial wireless communication system assigns two (or more) communication channels to each communication link, one as the preferred channel and the other as the backup channel, and negotiates the length of the receiving waiting time of both parties in a communication time slot at the same time. As shown in Figure 1, at the beginning of a given communication time slot, both the sender and the receiver choose the preferred channel for communication. If the communication channel is interfered, the sender first monitors whether the channel is idle through the CCA mechanism before sending data. If If the channel is busy, it will be considered that the communication channel is disturbed and no data will be sent. When the CCA monitoring time expires, the sender will adaptively generate and execute a channel switching control command; the receiver will always monitor the channel. If the data from the sender is not received, the receiver of the communication determines that the channel is interfered and immediately generates and executes a channel switching control command to switch the communication from the preferred channel to the standby signal, and the sender and the receiver jump to the standby signal simultaneously. channel, after a channel switching period, a new round of communication process starts. The sender will conduct channel monitoring again on the backup channel, and if the backup channel is not disturbed, it will immediately send data through the backup channel to complete the communication; if the channel is also interfered, it can only give up the communication of this time slot. The above-mentioned channel detection and channel switching are completed within one allocated time slot, without additionally occupying other time slots. The control command for channel switching is generated and executed by the two parties themselves, instead of one party sending the control command to the other party, so as to realize the self-adaptive channel hopping of both parties.

In order to make the technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below in combination with specific implementation examples and with reference to the accompanying drawings.

The IEEE 802.15.4 standard is a low-power, low-speed PHY/MAC standard. The IEEE802.15.4 physical layer provides a Clear Channel Assessment (CCA, Clear Channel Assessment) function. In the IEEE 802.15.4 physical layer standard protocol, the following three modes are defined for clear channel evaluation: CCA mode 1: energy exceeding the threshold, when CCA detects a threshold energy exceeding the energy detection, a busy Information. CCA mode 2: Carrier judgment, when CCA detects an extended modulation signal with IEEE 802.15.4 standard characteristics, it will give a busy message. CCA mode 3: Carrier judgment with energy exceeding the threshold value, when CCA detects an extended modulation signal with IEEE 802.15.4 standard characteristics and energy exceeding the threshold value, it will give a busy message. Therefore, the CCA mechanism of IEEE802.15.4 can be used to perform channel detection between sending data to confirm whether the channel is interfered. This implementation example takes working in CCA mode 1 as an example.

The IEEE 802.15.4 standard specifies 16 channels numbered from 11 to 26 at 2.4GHz. The communication parties that conform to the IEEE 802.15.4 standard can select a channel from the 16 channels for data communication. This implementation example takes a wireless device that complies with the IEEE 802.15.4 standard and operates in the 2.4GHz frequency band as an example to describe in detail as follows:

In order to improve the utilization rate of the channel in the existing industrial wireless network system, the length of the communication time slot is usually just enough for a complete communication, but to implement the method of the present invention, it is necessary to reserve time for the second communication in a short time. In the existing time slot length, time can be saved through the following two main methods: (1) reducing time error; (2) shortening the waiting time for receiving data. Both of these two measures need to be based on an accurate and efficient time synchronization method. Therefore, the present invention proposes a receiver-based time synchronization method for intra-slot self-adaptive channel hopping communication. In this method, the sender does not need to record a time stamp when sending, and then wirelessly sends to the other party, which can reduce the amount of data transmission and thus reduce power consumption. According to the time slot length structure T _Slot , the time when the first bit arrives at the receiver T _Arrival and the transmission and transmission offsets T _TxOffset1 , T _TxOffset2 , the algorithm module calls formula 1 to determine the start time of the next time slot to achieve time synchronization .

As shown in Figure 1, if the sender of the communication in the time slot is a clock source, then for each arriving data frame, the receiver records the arrival time of the first bit (T _Arrival ) and calculates the next time according to formula 1 The start time (T _Nextslot ) of the next slot (Next Slot), so as to realize the time synchronization of the slot communication. Due to the strict time slot length structure (T _Slot ) of the industrial wireless network, the receiver can start to confirm the start of the next time slot according to the following formula according to the arrival time of the data frame, where the sending offset T _TxOffset1 can be set to 1 and the sending The offset T _TxOffset 2 is a fixed value such as 2. If there is no adaptive channel hopping between the two sides of the time slot communication, the value T _TxOffset1 in formula 1 is taken; if channel switching occurs, the value T _TxOffset2 in formula 1 is taken. Time synchronization not only occurs during the normal data communication process of nodes, but also during the joining process of new nodes. The present invention follows the communication slot model as shown in FIG. 1 . When the channel is interfered, the sender performs the following function sub-slots: CCA error, CCA monitoring, idle, channel switching, CCA monitoring, sending data, waiting, receiving ACK. The receiver completes corresponding functions in the following function sub-slots: waiting for receiving data, channel switching, waiting for receiving data, reading data, data processing and verification, and sending ACK. The waiting time for receiving data in the time slot is determined by the length of the sending data, and the time error time must be kept within the specified range.

The present invention can be based on a variety of different physical frequency bands and standards. This implementation example takes the 2.4GHz frequency band in the standard IEEE 802.15.4 physical layer as an example for illustration, but is not limited thereto.

Before the communication, two communication channels are allocated for this communication time slot (if channel 13# is used as the preferred channel, and channel 20# is used as the standby channel). Before the data communication between the sender and the receiver, the sender first detects whether the preferred channel 13# is interfered by CCA in the CCA monitoring time slot. If the channel is always busy within the specified CCA detection time (T _sCCA ), then The sender thinks the channel is disturbed. In this implementation example, it is assumed that channel 13# is interfered, so the sender does not send data, and automatically switches the channel to channel 20#, and then performs CCA detection again to detect whether channel 20# can communicate, as in this channel When available, it switches from the CCA detection state to the sending state, and prepares to send data, and then the two parties communicate on this spare channel 20# for data communication.

If the receiving party does not receive the data sent by the sender within the specified data receiving waiting time, it also considers that channel 13# may be interfered and unavailable, and the receiving party automatically switches the channel to the standby channel 20# and continues to wait for receiving data. After receiving the data normally on the standby channel, the receiver reads the data and performs processing and verification, and sends an ACK to the sender after completion. All the above-mentioned processes are completed within the allocated time slots, without additionally occupying other time slots. The control command of channel switching is judged by the two parties in communication according to the channel state, and is generated and executed within a specified time, instead of one party sending a control command to the other party, so as to realize the true sense of self-adaptive channel hopping between the two parties.

The communication parties can switch the communication back to the preferred channel in the future communication time slots, use the preferred channel for communication, and continue to use the preferred channel 13# firstly. According to the above method, if the channel is detected to receive interference, it will adaptively jump to channel 20 # Perform data communication. Another method is: the communication parties will no longer give priority to using channel 13# in the future communication time slots, but give priority to using channel 20#, that is, channel 20# becomes the preferred channel and channel 13# becomes the standby channel .

The sender processing flow chart is shown in Figure 2. When the time slot communication starts, the sender first performs CCA to detect whether the channel is idle. If the channel is idle, the sender switches to the sending state and prepares to send data; if the channel is busy, it indicates that there may be other interference signals on the channel, and the sender generates the signal by itself. And execute the channel switching control command, and continue to execute CCA to detect whether the channel is idle after switching to a new channel. If the channel is still not idle, give up the communication and enter the dormant state to save power consumption; if the channel is idle at this time, switch to the sending state and prepare to send data. After the data is sent, it will sleep for a period of time so that the other party can process the data, and finally the sender wakes up Receive acknowledgment frame.

The flow chart of the receiver processing is shown in Figure 3. When the time slot communication starts, the receiver first listens to the channel to check whether it has received data, if so, it will continue to receive data until it is completed, then perform data processing and verification, and send a confirmation frame to the sender; if no data is received, then Continue to listen to the channel, if no data is received within the given receiving waiting time, it will be considered that the channel is interfered, and the channel switching control command will be generated and executed by itself, switch to a new channel, continue to listen to the channel, and prepare for receiving data Prepare, in the second waiting time to receive data, if data is received, then perform data processing and verification, and return a confirmation frame to the sender; if still not received data, give up the communication and enter the dormant state until the time slot Finish.

The specific embodiments described above have further described the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above descriptions are only specific embodiments of the present invention and are not intended to limit the present invention. Any modification, equivalent replacement, improvement, etc. made within the methods and principles of the present invention shall be included within the protection scope of the present invention.

Claims (3)

1. An industrial wireless communication method based on self-adaptive hopping channels in time slots, assigning preferred channels and standby channels for each communication link, characterized in that, time synchronization is carried out in preferred channels or standby channels, before the start of time slot communication After negotiating the CCA detection time length and the waiting time length for receiving data in the time slot, the sender uses the CCA mechanism to monitor the communication channel. If the preferred channel is interfered and the channel is always busy during the CCA monitoring time of the time slot, it will automatically switch To send data to the backup channel, the receiver does not receive the data from the sender after the specified waiting time, and automatically jumps from the preferred channel to the backup channel in this time slot to wait for receiving data. 2. The industrial wireless communication method according to claim 1, wherein said performing time synchronization specifically comprises, according to the time slot length structure T _Slot , the time T _Arrival of the first bit arriving at the receiver and the transmission offset T _TxOffset1 , T _TxOffset2 , the algorithm module calls formula 1 to determine the start time of the next time slot,

formula one 3. The industrial wireless communication method according to claim 1, characterized in that, in the subsequent communication time slot after channel hopping is completed, the standby channel that was successfully communicated last time is preferentially used as the current preferred channel, and both parties in the same time slot can communicate according to Adaptive channel selection in response to environmental changes.

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